Multiplexing redo log files

I am using 9i R2 database.
I just want to clear some doubts.
I am having 3 redo log groups with one member each.
Now for mutiplexing redo log files
i want to add one one member to each group so
that each group will have 2 members in some different path.
my current path of log member are
/oracle/files/a1.log (group 1)
/oracle/files/b1.log (group 2)
/oracle/files/c1.log (group 3)
I want to add
/oracle/sysfiles/a2.log (group 1)
/oracle/sysfiles/b2.log (group 2)
/oracle/sysfiles/c2.log (group 3)
A--So is there any need to take database in any mode (nomunt,mount) or i can do it while
database is open ?
I will issue
ALTER DATABASE ADD LOGFILE MEMBER /oracle/sysfiles/a2.log TO GROUP 1 ;
First in inactive group,then
alter system switch logfile; (To make 2 group inactive....and then 3)
B-- All memebers in a redolog group must be of same size? if i am having
100 M.B. of one member(a1.log) is there no need to specify size while adding new member(a2.log)?
Can some one validate and correct my steps or suggest me regarding this?

Hi,
All the solutions are in oracle documentaiton.
See, Members of the same multiplexed redo log group must be the same size (that all member in with in the group ) and Members of different groups can have different sizes. If the same of Files are different resultant would be the with Checkpoints. Since you can not gurantee that Checkpoints will occur at regular internals (Log switch with respect log members). Better to follow the Rules of traffic similarly follow the instrcutions of ORACLE Documentation.. :-)
- Pavan Kumar N

Similar Messages

Multiplexing Redo Log Files question

If you are running RAC on ASM on a RAID system, is this required? We are using an HP autoraid which mirrors at the block level and in the documentation about Multiplexing Redo Log Files it says that you do it to protect against media failure. The autoraid that we are using gives us multiple levels of redundancy against media failure so I was wondering if Multiplexing would be adding more overhead than is needed. Thanks for your input.

ASM is quite compex and I'm not going to outline all the advantages or reasons for ASM, but under ASM you can drop and add devices to maintain your capacity needs online without loosing data, which you cannot do using RAID, which requires a re-initialize, for example, regardless of redundancy. Please see the documentation. ASM, like pretty much everything Oracle will add complexity and you will have to check your requirements. ASM is however pretty much the standard. If you use external RAID, make sure your storage is not using RAID 5 or 0. Regarding logical errors, you could for example overwrite or delete a file by mistake, in which case file redundancy does not protect you. If you are looking for reasons or ways not to use ASM, I'm sure you will find them, but what's the point?

Multiplexing Redo Log and maximum protection mode.

Assume that during writing into redo logs the instance crashes. As a result, members of active redo group are not synchronized, some of them had more data. How Oracle will handle this when instance starts? And there can be case when at startup time some members that had more redo before crash, are lost.
Now assume that we have standby database with maximum protection mode. After LGWR has written to local redo logs and before writing to standby redo logs, primary instance crashes. In this case standby site lost last transaction.
Is it correct? Thanks.

Assume that during writing into redo logs the instance crashes. As a result, members of active redo group are not synchronized, some of them had more data. How Oracle will handle this when instance starts? And there can be case when at startup time some members that had more redo before crash, are lost.
Members of a particular group are written concurrently by LGWR, all members of a log group will have same data. If any member of a particular group is lost or not reachable, oracle will read from the available log member during instance recovery.
Multiplexing Redo Log Files
http://docs.oracle.com/cd/B19306_01/server.102/b14231/onlineredo.htm#i1006249
To answer your second question,In this mode no transaction commits on primary unless the redo is also written on atleast one standby database, otherwise primary will go down.
Check below
Maximum Protection
http://docs.oracle.com/cd/B28359_01/server.111/b28294/protection.htm#CHDHFHJI

How does LGWR write redo log files, I am puzzled!

The document says:
The LGWR concurrently writes the same information to all online redo log files in a group.
my undestandint of the sentence is following for example
group a includes file(a1, a2)
group b includes file(b1, b2)
LGWR write file sequence: write a1, a2 concurrently; afterwards write b1, b2 concurrently.
my question is following:
1、 my understanding is right?
2、 if my understanding is right, I think that separate log file in a group should save in different disk. if not, it cann't guarantee correctly recovery.
my opinion is right?
thanks everyone!

Hi,
>>That is multplexing...you should always have members of a log file in more than 1 disk
Exactly. You can keep multiple copies of the online redo log file to safeguard against damage to these files. When multiplexing online redo log files, LGWR concurrently writes the same redo log information to multiple identical online redo log files, thereby eliminating a single point of redo log failure. In addition, when multiplexing redo log files, it is preferable to keep the members of a group on different disks, so that one disk failure will not affect the continuing operation of the database. If LGWR can write to at least one member of the group, database operation proceeds as normal.
Cheers
Legatti

ASM Environment multiplexed redo logs

When we have multi diskgroups like ('+DATA','+FLASH) and configured to multiplexed redologs on asm environment what would be the performance impact while logwriter writing on multiple locations? The diskgroups have different number disks on each diskgroup. Like 100 vs 10 disks on diskgroup.

http://download.oracle.com/docs/cd/B19306_01/server.102/b14231/onlineredo.htm
Multiplexing Redo Log Files help protect against a failure involving the redo log itself.
after you implement, you should check AWR report about waiting.
On ASM, you don't need to make multiple redo files. Just place it (redo file) in good i/o diskgroup (RAID1/0)

Multiplex Redo Logs and Control File

I am wanting to setup an existing Oracle Express 10g instance to multiplex the redo log files and the control file.
Instance is using Oracle-Managed Files and the Flash Recovery Area.
With these options being used what are the steps required to setup multiplexing?
I tried setting the DB_CREATE_ONLINE_LOG_DEST_1 and DB_CREATE_ONLINE_LOG_DEST_2 parameters but this doesn't appear to have worked (I even bounced the db instance).
BTW, the DB_CREATE_FILE_DEST is set to null and the DB_RECOVERY_FILE_DEST is set to the flash recovery area.
Any help is much appreciated.
Regards, Sheila

Thanks for this. My instance originally had two log groups so I've added a new member to each group into the same flash recovery area directory, but have assigned a name. Is this why when I query v$logfile the is_recovery_dest_file is set to NO? Is it ok to assign a name & directory and if not, how do you add a new memeber and allow Oracle-Managed files to name them?
Also, how can I check that the multiplexing is working (ie the database is writing to both sets of files)?
Thanks again.

Non-multiplexed online redo log file damaged

how to fix if non-multiplexed online redo log file damaged , looking for info for both current & inactive..

If you only want to practice your skills these are good scenarios to do it. But if you are currently facing this problem then you are in big troubles if it happens to be the CURRENT. When this issue appears I suggest you not to shutdown the instance you should be aware that information written on the redo log is the backup of the running transactions in memory. If both get lost data is lost, if either one survives your chances to recover data are high.
~ Madrid
http://hrivera99.blogspot.com

Standby redo log file

Hi,
From oracle document i know in the standby side the RFS process writes to Standby redo log file -> archive log and the MRP procees applys the archive logs to the standby database.
my question is ,if we dont create standby redo log file what happens?

Hello;
When redo is received by an RFS on the standby , the RFS process writes the redo data into archived redo logs or optionally to the SRL.
Standby Redo Logs is where the RFS process at your Standby database writes incoming redo, they help performance because the RFS does not have to create the Archive log file.
Standby redo logs are a component of the Data Guard setup. They should be the same size as the redo logs on the Primary.
Standby Redo Logs do not not to be multiplexed.
I would create SRL them on both the Primary and the Standby. Think of it as one database in either Standby or Primary Mode. If you have to switchover you still need them.
If you have SRL's setup and need to do either a failover or switchover it should occur faster and safer.
Best Regards
mseberg

What is the purpose of standby redo log files

Hi,
What is the purpose of the standby redo log files in DR?
what if the standby redo log files are created? or else not created?
Please explain
Thanks

3.1.3 Configure a Standby Redo LogA standby redo log is required for the maximum protection and maximum availability modes and the LGWR ASYNC transport mode is recommended for all databases. Data Guard can recover and apply more redo data from a standby redo log than from archived redo log files alone.
You should plan the standby redo log configuration and create all required log groups and group members when you create the standby database. For increased availability, consider multiplexing the standby redo log files, similar to the way that online redo log files are multiplexed.>
Reference http://download.oracle.com/docs/cd/B19306_01/server.102/b14239/create_ps.htm#i1225703
HTH
Anand

Use of standby redo log files in primary database

Hi All,
What is the exact use of setting up standby redo log files in the primary database on a data guard setup?
any good documents?

A standby redo log is required for the maximum protection and maximum availability modes and the LGWR ASYNC transport mode is recommended for all databases. Data Guard can recover and apply more redo data from a standby redo log than from archived redo log files alone.
You should plan the standby redo log configuration and create all required log groups and group members when you create the standby database. For increased availability, consider multiplexing the standby redo log files, similar to the way that online redo log files are multiplexed.
refer the link,and Perform the following steps to configure the standby redo log.:-
http://download.oracle.com/docs/cd/B19306_01/server.102/b14239/create_ps.htm#i1225703
If the real-time apply feature is enabled, log apply services can apply redo data as it is received, without waiting for the current standby redo log file to be archived. This results in faster switchover and failover times because the standby redo log files have been applied already to the standby database by the time the failover or switchover begins.
refer the link
http://download.oracle.com/docs/cd/B19306_01/server.102/b14239/log_apply.htm#i1023371

Bottleneck when switching the redo log files.

Hello All,
I am using Oracle 11.2.0.3.
The application team reported that they are facing slowness at certain time.
I monitored the database and I found that at some switching of the redo log files (not always) I am facing a slowness at the application level.
I have 2 threads since my database is RAC, each thread have 3 redo log groups multiplexed to the FRA, with size 300 MB each.
Is there any way to optimize the switch of redo log files? knowing that my database is running in ARCHIVELOG mode.
Regards,

Hello Nikolay,
Thanks for your input I am sharing with you the below information. I have 2 instances so I will provide the info from each instance
Instance 1:
Load Profile              Per Second    Per Transaction   Per Exec   Per Call
~~~~~~~~~~~~         ---------------    --------------- ---------- ----------
      DB Time(s):                4.9                0.0       0.00       0.00
       DB CPU(s):                1.1                0.0       0.00       0.00
       Redo size:        3,014,876.2            3,660.4
   Logical reads:           32,619.3               39.6
   Block changes:            7,969.0                9.7
Physical reads:                0.2                0.0
Physical writes:              164.0                0.2
      User calls:            7,955.4                9.7
          Parses:              288.9                0.4
     Hard parses:               96.0                0.1
W/A MB processed:                0.2                0.0
          Logons:                0.9                0.0
        Executes:            2,909.4                3.5
       Rollbacks:                0.0                0.0
Instance 2:
Load Profile              Per Second    Per Transaction   Per Exec   Per Call
~~~~~~~~~~~~         ---------------    --------------- ---------- ----------
      DB Time(s):                5.5                0.0       0.00       0.00
       DB CPU(s):                1.4                0.0       0.00       0.00
       Redo size:        3,527,737.9            3,705.7
   Logical reads:           29,916.5               31.4
   Block changes:            8,893.7                9.3
Physical reads:                0.2                0.0
Physical writes:              194.0                0.2
      User calls:            7,742.8                8.1
          Parses:              262.7                0.3
     Hard parses:               99.5                0.1
W/A MB processed:                0.4                0.0
          Logons:                1.0                0.0
        Executes:            2,822.5                3.0
       Rollbacks:                0.0                0.0
    Transactions:              952.0
Instance 1:
Top 5 Timed Foreground Events
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                                           Avg
                                                          wait   % DB
Event                                 Waits     Time(s)   (ms)   time Wait Class
DB CPU                                            1,043          21.5
log file sync                       815,334         915      1   18.9 Commit
gc buffer busy acquire              323,759         600      2   12.4 Cluster
gc current block busy               215,132         585      3   12.1 Cluster
enq: TX - row lock contention        23,284         264     11    5.5 Applicatio
Instance 2:
Top 5 Timed Foreground Events
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                                           Avg
                                                          wait   % DB
Event                                 Waits     Time(s)   (ms)   time Wait Class
DB CPU                                            1,340          24.9
log file sync                       942,962       1,125      1   20.9 Commit
gc buffer busy acquire              377,812         594      2   11.0 Cluster
gc current block busy               211,270         488      2    9.1 Cluster
enq: TX - row lock contention        30,094         299     10    5.5 Applicatio
Instance 1:
Operating System Statistics        Snaps: 1016-1017
-> *TIME statistic values are diffed.
   All others display actual values. End Value is displayed if different
-> ordered by statistic type (CPU Use, Virtual Memory, Hardware Config), Name
Statistic                                  Value        End Value
AVG_BUSY_TIME                             17,451
AVG_IDLE_TIME                             81,268
AVG_IOWAIT_TIME                                1
AVG_SYS_TIME                               6,854
AVG_USER_TIME                             10,548
BUSY_TIME                                420,031
IDLE_TIME                              1,951,741
IOWAIT_TIME                                  288
SYS_TIME                                 165,709
USER_TIME                                254,322
LOAD                                           3                6
OS_CPU_WAIT_TIME                         523,000
RSRC_MGR_CPU_WAIT_TIME                         0
VM_IN_BYTES                              311,280
VM_OUT_BYTES                          75,862,008
PHYSICAL_MEMORY_BYTES             62,813,896,704
NUM_CPUS                                      24
NUM_CPU_CORES                                  6
NUM_LCPUS                                     24
NUM_VCPUS                                      6
GLOBAL_RECEIVE_SIZE_MAX                4,194,304
GLOBAL_SEND_SIZE_MAX                   4,194,304
TCP_RECEIVE_SIZE_DEFAULT                  16,384
TCP_RECEIVE_SIZE_MAX      9.2233720368547758E+18
TCP_RECEIVE_SIZE_MIN                       4,096
TCP_SEND_SIZE_DEFAULT                     16,384
TCP_SEND_SIZE_MAX         9.2233720368547758E+18
TCP_SEND_SIZE_MIN                          4,096
Operating System Statistics - Detail Snaps: 1016-101
Snap Time           Load    %busy    %user     %sys    %idle %iowait
22-Aug 11:33:55      2.7      N/A      N/A      N/A      N/A      N/A
22-Aug 11:50:23      6.2     17.7     10.7      7.0     82.3      0.0
Instance 2:
Operating System Statistics         Snaps: 1016-1017
-> *TIME statistic values are diffed.
   All others display actual values. End Value is displayed if different
-> ordered by statistic type (CPU Use, Virtual Memory, Hardware Config), Name
Statistic                                  Value        End Value
AVG_BUSY_TIME                             11,823
AVG_IDLE_TIME                             86,923
AVG_IOWAIT_TIME                                0
AVG_SYS_TIME                               4,791
AVG_USER_TIME                              6,991
BUSY_TIME                                475,210
IDLE_TIME                              3,479,382
IOWAIT_TIME                                  410
SYS_TIME                                 193,602
USER_TIME                                281,608
LOAD                                           3                6
OS_CPU_WAIT_TIME                         615,400
RSRC_MGR_CPU_WAIT_TIME                         0
VM_IN_BYTES                               16,360
VM_OUT_BYTES                          72,699,920
PHYSICAL_MEMORY_BYTES             62,813,896,704
NUM_CPUS                                      40
NUM_CPU_CORES                                 10
NUM_LCPUS                                     40
NUM_VCPUS                                     10
GLOBAL_RECEIVE_SIZE_MAX                4,194,304
GLOBAL_SEND_SIZE_MAX                   4,194,304
TCP_RECEIVE_SIZE_DEFAULT                  16,384
TCP_RECEIVE_SIZE_MAX      9.2233720368547758E+18
TCP_RECEIVE_SIZE_MIN                       4,096
TCP_SEND_SIZE_DEFAULT                     16,384
TCP_SEND_SIZE_MAX         9.2233720368547758E+18
TCP_SEND_SIZE_MIN                          4,096
Operating System Statistics - Detail Snaps: 1016-101
Snap Time           Load    %busy    %user     %sys    %idle %iowait
22-Aug 11:33:55      2.6      N/A      N/A      N/A      N/A      N/A
22-Aug 11:50:23      5.6     12.0      7.1      4.9     88.0      0.0
          -------------------------------------------------------------

Commit Completes although current online redo log file have been removed.

Although i have removed current online redo log file in linux os (Oracle Linux),when i type "commit" it says that "commit complete".
Is this fair for this princip?*:" if Only when all redo records associated with a given transaction are safely on disk in the online logs is the user process notified that the transaction has been committed."*
I think that it can lead to loss of data in some cases..I'm using Oracle 11g R2 on OEL (x64)..
Can anyone explain me ? I'm getting stuck in this situation..
P.S : I haven't multiplexed current ORL group files...

Javid wrote:
Although i have removed current online redo log file in linux os (Oracle Linux),when i type "commit" it says that "commit complete".
Is this fair for this princip?*:" if Only when all redo records associated with a given transaction are safely on disk in the online logs is the user process notified that the transaction has been committed."*
I think that it can lead to loss of data in some cases..I'm using Oracle 11g R2 on OEL (x64)..
Can anyone explain me ? I'm getting stuck in this situation..
In *nix, a file that is open by a process isn't really deleted until the process that has it completes. So even though you 'deleted' a redo log, oracle is still holding it. As soon as you stop your database (maybe even as soon as the db does a log switch) the redo will really be gone and no longer available. consider the implications for archive logging.
P.S : I haven't multiplexed current ORL group files...You need to fix that. the online logs are the achilles heel of the database. That's why it is standard practice to multiplex them.

Recover from missing files(redo log file/control file) and state of the DB

Hello,
i hv go through the doc. as well. But have some doubts what will happen in each on these situations.
Pls help me to clarify these!
Scenario is like this;
hv 3 redo log files - multiplxed
hv 3 control files - multiplxed
- What will happen if 1 redo log file missing when starting the DB?
- What will happen if 1 redo log file missing when using(performing operations) the DB?
(will it recover automatically/db abort/even redo log lost will the DB run as usual... ?)
-How to recover this lost redo log?
- What will happen if 1 control file missing when starting the DB?
- What will happen if 1 control file missing when using(performing operations) the DB?
(will it recover automatically/db abort/even control file lost will the DB run as usual... ?)
-How to recover this lost redo log?
thanks

- What will happen if 1 redo log file missing when starting the DB?IF you have multiplexed the members you can drop the lost file and will be able to open the DB
What will happen if 1 redo log file missing when using(performing operations) the DB?Again if multiplexed it will drop a warinign in the alert log and contnue to write on othere members
http://download.oracle.com/docs/cd/B19306_01/backup.102/b14191/recoscen.htm#sthref1385
- What will happen if 1 control file missing when starting the DB?Just remove the entry from the init.ora and start the DB
What will happen if 1 control file missing when using(performing operations) the DB?Will shutdown

Redo log file corupted, database not getting open

I am Oracle Funda-1 student.
Have install standard Oracle 9I on Windows XP pro service pack 2.
I made some changes in sample table & given commit. So log buffer will flush to redo log file.
Then I open current redo log file from OS & selected all junk characters [select all] & deleted same. Save the file. Causing redo file size 0KB.
Then made more changes to table & issue commit. no errors ! every thing working file.
Even chked V$log & V$logfile.
Again I open current redo log file from OS & selected all junk characters [ select all ] & deleted same. Save the file. Causing redo file size 0KB.
Then issue manual log switch. Alter system switch logfile
I got disconnected from database & database was close.
When I reconnected & try to open database in normal mode. Gave error saying redolog_1.log is corrupted & needed for recovery.
Now not even allowing me clear redo group 1. with alter database clear logfile group 1. as database is not coming to open stage.
just able to mount the database. with error rdolog_1 corrupted.
Wasn't oracle suppose to be halted when very 1st time I corrupted redo log file.
Why it disconnected me & got close.
When then one use alter database clear logfile group 1.

I may try this ALTER DATABASE OPEN RESETLOGS;
As no backup & not multiplex.
Still looking for explanation why database got close down instead of getting halt.
I have found one more status in V$log, which is not given in Oracle university book or online document.
INVALIDATED
Which come as a result when oracle unable to switch to next on line group due to non availability of next group redo log physical file.
SQL> select group#,members,status from V$log;
GROUP# MEMBERS STATUS
1 1 INVALIDATED
2 1 INACTIVE
4 1 UNUSED
As matter of fact, it's only portion of a big
document which happen to cover what you are testing
in detail.
I would invest time to read the document to
understand how things work instead of getting dirty
quick answers.

Why multiplex redo log group ?

Hello,
Why should we multiplex redo log groups if we have only file system which is already mirrored. Is there any one who had an incident when he has only one redo log member per group placed on a mirrored file system but still got corrupted and he felt better to have multiple members even if they reside on the same file system (which is mirrored)
Thanks
Salman

Ansiktet wrote:
EdStevens wrote:
Salman Qureshi wrote:
Hello,
Why should we multiplex redo log groups if we have only file system which is already mirrored. Is there any one who had an incident when he has only one redo log member per group placed on a mirrored file system but still got corrupted and he felt better to have multiple members even if they reside on the same file system (which is mirrored)
Thanks
SalmanThe mirror won't protect you from an SA who deletes '/u01/oradata/redo01.log' because he is running out of space on /u01 and figures its safe to delete a log file.
Or similar types of errors.
The redo and control files are simply too critical to put all your eggs in one basket when planning their protection.:) Thats why you should not use Oracle default .log on redo, instead .dbf or .dbl can be used. THat's why I use the older (pre-10g) default of .rdo for redo logs
However, has this happend anyone for real, that a SA delete Oracle files? Where do you think I came up with the example?
HOw about an SA (or maybe the kind of "fresher" we often see here, Taking a look at a "log" file with notepad?
If he is isnt stupid he should know that Oracle resides on /u01 partion (for example), and should not delete files there without consulting the DBA."should" is the operative word there. There is no accounting for corporate cultures and attitudes.
But end the end, my example was to illustrate that not all problems with redo and control files are mitigated with disk mirroring.

Multiplexing redo log files

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